This invention relates generally to a liquid supply system, and more specifically, it relates to a system for supplying a liquid at a substantially constant pressure.
While the following description relates primarily to a domestic water supply system, it will be apparent that the invention is also applicable to other types of liquid supply systems.
A domestic water supply system in common use includes a motor-pump unit located in a water well, the unit being suspended by a pipe which also conveys the pumped water to the house. At the surface, the system further includes a storage-pressure tank which receives the pumped water and is connected to the plumbing of the house. A water pressure actuated switch is mounted adjacent to the tank through which electric power is supplied to the motor. Hysteresis in the operation point of this switch establishes an operating pressure range for the tank and water supply system. The electric motor is a constant speed type and the pump is usually a centrifugal type. The storage tank is relatively large (usually about 15 to 30 gallons) and stores a sizable amount of water, so that the motor does not have to be turned on and off frequently.
Systems similar to the foregoing have included a jet pump in place of the centrifugal pump, and this arrangement is useful with relatively small diameter pipes. However, jet pumps are usually avoided because they have a lower efficiency than centrifugal pumps.
Another type of water supply system includes a variable speed motor and a centrifugal pump. The power supply for the motor includes a DC link electronic package which varies the motor speed in response to the water pressure. In another type of system, an electronic package is part of the motor-pump unit so that the heat-generating electronic package may be cooled by the well water. Systems including a pressure sensor and a variable speed motor and designed to supply water at a substantially constant pressure have also been provided. Such systems have been used as pressure boosters in relatively tall buildings in some areas (usually outside the United States).
It is a general object of the present invention to provide a system for supplying a liquid at a substantially constant pressure which is an improvement over the foregoing systems.